cmd/link, cmd/internal/obj: stop exporting various names

cmd/link, cmd/internal/obj: stop exporting various names

Just happened to notice that these names (funcAlign and friends) are
never referenced outside their package, so no need to export them.

Change-Id: I4bbdaa4b0ef330c3c3ef50a2ca39593977a83545
Reviewed-on: https://go-review.googlesource.com/31496
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>